Studies will be continued the aim of which is to characterize the actions of sex steroids on nucleic acid metabolism in the brains of neonatal and pubertal rats. These changes, depending on age at the time of administration, accompany either permanent or temporary, or no changes in brain differentiation and function. A second area of study is directed toward analysis of the action of hormones on the nervous system of male frogs during the time male sex behavior is evoked by the hormone treatment. In particular, changing stimulus thresholds in the rostral preoptic hypothalamic areas will be explored. BIBLIOGRAPHIC REFERENCES: Farquhar, M., Namiki, H. and Gorbman, A. 1975. Accumulation of 3H-testosterone in nuclear and cytoplasmic fractions of rat brain during postnatal development. Neuroendocrinology, 20:136-150. Wada, M., Wingfield, J., and Gorbman, A. 1976. Correlation between blood level of androgens and sexual behavior in male leopard frogs, Rana pipiens. Gen. Comp. Endocrinol., 29:72-77.